The present invention relates to an MIS type semiconductor integrated circuit device with a refractory metal gate electrode.
Devices of this general type are already known in the art. A conventional method for fabricating such a device will be described below with reference to FIG. 1 which shows, in cross section, an MIS device composed of an N-type monocrystalline silicon substrate 11 in which are formed P.sup.+ diffusion zones 15, a field insulation film 12, a gate insulation film 13, a refractory metal film gate electrode 14, an interlayer insulation film 16 and aluminum contact members 17. Zones 15 constitute a source region and a drain region
In the structure shown above, refractory metal film gate electrode 14 is easily polluted by the resist film and an organic solvent after the electrode is formed, thereby causing variations in, and instability of, the threshold voltage. At the same time, the electrode is weak due to having been chemically treated with acid. Further, the refractory metal film electrode is easily polluted and oxidized if oxygen and moisture are present in the atmosphere of the heat-treatment.
A solution to the above-described problems is suggested in Japan Laid-Open Patent No. 58-46651, which discloses forming a silicon layer with an oxidized surface or a refractory metal silicide layer with an oxidized surface on the side and the top surface of the refractory metal film gate electrode.
In an MIS type semiconductor integrated circuit device as fabricated in accordance with the conventional technique described with reference to FIG. 1, the device has a refractory metal film forming the gate electrode and, therefore, the device is easily polluted by a resist film and an organic solvent, subject to damage due to chemical treatment using acid and so on, and easily oxidized if oxygen and moisture are present in the heat treatment atmosphere. Thus, the conventional MIS type semiconductor integrated circuit device is very inferior from the standpoint of reliability and yield.
The MIS type semiconductor integrated circuit device disclosed in Japan Laid-Open Patent No. 58-46651 has a little better characteristics than that having the structure shown in FIG. 1. However, it, too, has problems. This MIS type semiconductor integrated circuit device employs a refractory metal film gate electrode having a resistance which is more than two orders of magnitude, i.e., 10.sup.2, lower than a polycrystalline silicon layer as a gate electrode. Therefore, the breakdown voltage of the gate is made lower, having high potentiality causing breakdown of the gate insulation film and leakage of electric current or a short circuit between the gate electrode and the semiconductor substrate. The leakage of electric current and the short circuit caused between the gate electrode and the semiconductor substrate are considered to be due to the metal from the refractory metal film reaching the substrate and penetrating through the gate insulation film, refractory metal having a very low resistance being used as the gate electrode. In addition, the coefficient of thermal expansion of the refractory metal film is different from that of the gate insulation film.
Because of this phenomena, the gate insulation film is broken down, thereby causing leakage of electric current and short circuits between the gate electrode and the semiconductor substrate.
It is currently known to employ electrodes composed of two layers of silicide and polycrystalline silicon as the gate electrode for an MIS device. However, such a material is associated with a high electrical resistance, which presents serious problems, particularly when highly integrated circuits are to be produced. In order to reduce this resistance as much as possible, it is presently considered essential to employ refractory metal for electrodes. However, the electrode material employed must be compatible with silicon gate processes and refractory metals have been found to be a source of instabilities during manufacture and to impair long term stability of the resulting integrated circuits.